But it emerged that Mr Roeder had a history of extreme hostility and suspicion towards the US government and later allegedly became dedicated to closing what he called Dr Tiller's "death camp".

In 1996, a district judge said Mr Roeder presented a "threat of danger to the public" after bomb-making equipment was found in his car along with a military rifle, gas mask and ammunition.

At the time, his father, John, described him as an "obsessed" but loving man who wouldn't "kill a fly".

Mr Roeder had been involved with the Freemen movement, an extreme Christian conservative and anti-government group – a link which prompted a district attorney to describe him as a "substantial threat to public safety".

The now-defunct Freemen, whose members refused to pay taxes and rejected the federal government's authority, were famously involved in an 81-day armed standoff with federal marshals in 1996.

Morris Wilson, a former commander of the Kansas Unorganised Citizens Militia, told the Kansas City Star that he remembered Mr Roeder as "a good ol' boy except he was just so fanatic about abortion".

The suspect, who was married for 10 years and has a son, is a former factory worker.

A man calling himself Scott Roeder posted several messages on the website of Operation Rescue, an anti-abortion group which has targeted Dr Tiller for years.

In one, he wrote: "Tiller is the concentration camp 'Mengele' of our day and needs to be stopped before he and those who protect him bring judgement upon our nation".

In another, he suggested activists should attend Dr Tiller's church "to have much more of a presence and possibly ask questions of the pastor, deacons, elders and members while there".

Troy Newman, Operation Rescue's president, said that Mr Roeder was "not a friend, not a contributor, not a volunteer" with the group.

The organisation, which moved its operation to Wichita so it could concentrate on Dr Teller's clinic, was quick to condemn the killing.

In a statement released by Mr Roeder's family, his brother, David, said: "We know Scott as a kind and loving son, brother and father who suffered from mental illness at various times in his life."

Clarence Roeder, the suspect's uncle, said that his family members were – like Dr Tiller – Lutherans "and that adds a double touch of sadness and irony".

Dave Leach, an anti-abortion activist from Iowa, said Mr Roeder had contributed to his newsletter, Prayer and Action News, which argues that killing abortionists is justifiable homicide.

Mr Leach said that to call Mr Tiller's death a crime was "too simplistic... there is Christian scripture that would support this".

He said he met the suspect once. "He told me about a lot of conspiracy stuff and showed me how to take the magnetic strip out of a five dollar bill," Mr Leach told the Kansas City Star. "He said it was to keep the government from tracking your money."